Apparatus for assembling potentiometer bridging contact device

ABSTRACT

A COIL-RECEIVING POST HAVING A FREE END IS PROVIDED WITH A RECESS HAVING AN INWARDLY CONVERGING SIDE WALL. THERE ARE MEANS FOR EFFECTING RELATIVE AXIAL MOVEMENT BETWEEN THE POST AND THE LATERALLY SPACED LEGS OF A LINEAR MOTION POTENTIOMETER SLIDE TO PRESS THE FREE ENDS OF THE LEGS AND THE CONVERGING SIDE WALL OF THE POST AGAINST EACH OTHER IN ORDER TO SQUEEZE THE LEGS TOGETHER TEMPORARILY. THERE ALSO ARE MEANS FOR MOVING A WIRE COIL AXIALLY OFF THE FREE END OF THE POST INTO POSITION AROUND THE SQUEEZED LEGS, AND MEANS FOR THEN SEPARATING THE POST FROM THE LEGS TO PERMIT THE FREE ENDS OF THE LEGS TO SPRING APART WITH THE WIRE COIL ENCIRCLING THEM.

M. W. BANG March 16, 197i APPARALUS FOR AJSEMBLING POTENTIOMETER BRIDGING CONTACT DEVICE 2 Sheets-Sheet 1 Filed D80. 23, 1968 M1 u, 2% M. W. BANG APPARATUS FOR ASSEMBLING POTENTIOMETER BRIDGING CONTACT DEVICE Filed Dec. 23, 1968 2 Sheets-Sheet 3 INVENTOR. MOGEA/S PM BAA/6 United States Patent 3,570,098 APPARATUS FOR ASEMBLING POTENTIOMETER BRIDGING CONTACT DEVICE Mogens W. Bang, Ridgway, Pa., assignor to Stackpole Carbon Company, St. Marys, Pa. Filed Dec. 23, 1968, Ser. No. 786,274 Int. Cl. Hk 13/04 US. Cl. 29-203 9 Claims ABSTRACT OF THE DISCLOSURE A coil-receiving post having a free end is provided with a recess having an inwardly converging side wall. There are means for effecting relative axial movement between the post and the laterally spaced legs of a linear motion potentiometer slide to press the free ends of the legs and the convernging side wall of the post against each other in order to squeeze the legs together temporarily. There also are means for moving a wire coil axially off the free end of the post and into position around the squeezed legs, and means for then separating the post from the legs to permit the free ends of the legs to spring apart with the Wire coil encircling them.

In one form of linear motion potentiometer a bridging contact is slid sideways along parallel resistor and collector strips, the contact being formed from a wire coil encircling a solid pin projecting between the strips from a slide. The free end of the pin is enlarged to hold the coil on the pin. Although such a bridging contact device is satisfactory in operation if the coil wire is not too fine, it does not lend itself very well to being assembled automatically by a machine. Also, the pin is rectangular in cross section which, as coils are made of smaller gage wire, causes some of the control of the position and movement of the coil to be lost.

It is among the objects of this invention to provide simple and inexpensive apparatus for assembling a bridging contact device of the general type just explained.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a plan view of the assembling apparatus;

FIG. 2 is a fragmentary side view, partly broken away in section, showing a slide in coil-receiving position;

FIG. 3 is an enlarged view showing a coil being applied to a slide;

FIG. 4 is a similar vie-w showing the next step in the operation;

FIG. 5 is a vertical section taken on the line VV of FIG. 2; and

FIG. 6 is an enlarged bottom View of the contact device.

Referring to the drawings, the bridging contact 1 for a linear motion potentiometer, such as shown in Pat. No. 3,362,004, where the contact is between a resistor strip and a collector strip and in engagement with both, is formed from a wire coil. In order to slide the coil along the strips, it is carried by a slide 2 slidably mounted in a longitudinal slot in one side of the potentiometer case. To support and move the coil, the slide is provided with a pair of substantially parallel laterally spaced legs 3 projecting from one side of the slide. The legs are spaced apart far enough to engage the inside of the coil at diametrically opposite points in an axial plane of the coil extending through both legs and across the space between them. This plane therefore extends lengthwise of the slide. The legs, in cross section, form portions of a common ellipse rather than being flat, so that each leg makes only a single line contact with the coil, as indicated in FIG. 6. The inner sides of the legs bordering the space between the legs are flat and have side edges spaced in- 3,579,098 Patented Mar. 16, 1971 ice wardly from the coil so that its convolutions can be tilted or skewed slightly by the resistor and collector strips engaging them in use, whereby to insure firm engagement with them.

At their free ends, the legs 3 are provided with small lateral projections 5 that form 'a pair of feet projecting away from each other. The feet are just large enough to prevent the coil from slipping off the legs. The legs have a little spring to them, so that their free ends can be squeezed toward each other to permit the coil to he slipped past the feet in assembling the coil and slide. Preferably, the slide is molded from a plastic.

In order to mount the coil on the pair of legs of the slide, the coil first is fitted over a post and then the post and legs are aligned and engaged, the free ends of the legs are squeezed toward each other, the coil is slipped axially off the post and onto the legs, and then the legs are al lowed to spring away from each other so that their feet will hold the coil in place. The apparatus for accomplishing all this, as shown in FIGS. 1 and 2, includes a support or table 7 that is mounted on a central vertical shaft 8 rotatably supported in any suitable manner. The shaft is turned intermittently by any well known type of drive, such as a Geneva mechanism (not shown). This indexes the table from station to station.

At uniformly spaced points around the table it is provided with vertical openings 10 therethrough. Slidably mounted in each of these openings is a post 11 that extends above and below the table. The upper portion of each post is enlarged so that it normally will rest on top of the table, and its upper end is provided with a recess 12 having a downwardly tapered side wall. The diameter of the upper portion of each post is only slightly smaller than the internal diameter of a coil 1, so that the coil can be slidably mounted on the post. The coils will not project above the posts.

At a loading station where the table stops momentarily, a coil is fed to the post 11 indexed to that station. This can be done by positioning the lower end of a feeding tube 14 directly over the post. The upper end of the tube receives coils from a suitable source of supply, such as a conventional coil winding machine (not shown). Every time a post arrives at the loading station, a coil slides down the tube and drops over the post. The tube is then turned a few degrees to index the coil carrying post laterally toward an assembly station, where the coil is to be applied to a slide 2.

At the assembly station there is means for holding a slide stationary above the post. A convenient Way of doing this is to use the means by which the slides are fed to the assembly station. For this double purpose a track may be used that extends horizontally across the table from a suitable source of supply of the slides. The track is formed from a pair of spaced parallel rails 16 that fit in grooves 17 (FIG. 5) in the opposite sides of the slides. The slides are pushed along the track end-to-end intermittently one slide length at a time by any suitable means. Each time they come to rest, one of them is located directly above a coil-encircled post at the assembly station, with its legs aligned with the post. Then, as shown in FIG. 2, the post is raised to press its upper end against the lower ends of the legs. The tapered side wall of the rising post recess 12 engages the downwardly converging outer surfaces of feet 5 and thereby squeezes to feet toward each other as the post continues to rise slightly farther. There are various ways in which to raise the post, but a simple way to do it is by means of a cam 18 mounted on a con tinuously rotating cam shaft 19. The lower end of the post rests on the cam and is raised and lowered by it.

While the slide legs above the raised post are sprung toward each other in the post recess, the underlying coil is stripped off the post and lifted up around the legs. This is done by means of a stripping ring 21 that encircles the post and normally rests on the table as shown in FIG. 2 and 5. The coil rests on the ring. At one side of the ring there is a stem 22 that extends from the ring down through a slot 23 in the table. The stem can be raised and lowered in the same manner as the post; e.g. by a cam 24 on cam shaft 19. When the stem lifts its ring, the ring pushes the coil up oil the post and around the slide legs as shown in FIG. 3. The feet do not interfere because they are in the post recess. While the ring remains in its upper position momentarily, the post is lowered as shown in FIG. 4, which allows the lower ends of the slide legs to spring apart and project their feet beneath the coil held above them by the ring, thereby locking the coil on the legs. Then the ring is lowered back to the table and the table is indexed to locate the next coil-encircled post at the assembly station. At the same time, the slides on the track are pushed along one slide length to remove the assembled slide from the assembly station and to move a new slide into coil-receiving position. Consequently, the contact devices can be quickly and automatically assembled.

I claim:

1. Apparatus for applying a wire coil contact to a pair of substantially parallel laterally spaced legs projecting from one side of a linear motion potentiometer slide, said apparatus comprising a coil-receiving post having a free end provided with a recess having an inwardly converging side wall, means for effecting relative axial movement between said slide legs and post to press the free ends of the legs and said converging side wall against each other in order to squeeze the legs together temporarily, means for moving a coil axially off said free end of the post and into position around the squeezed legs, and means for then reversing said axial movement to permit the free ends of the legs to spring apart.

2. Apparatus according to claim 1, including coil-receiving means for feeding a wire coil axially over said free end of the post and onto the post.

3. Apparatus according to claim 2, in which said post is upright and said coil-feeding means is a tube above the post for guiding a coil down to the upper end of the post.

4. Apparatus according to claim 2, in which said post is upright and the apparatus includes means for holding a slide stationary above the post, and said axial movementetfecting means include a cam for raising the post into engagement with the lower ends of slide legs above it.

5. Apparatus according to claim 2, in which said coilmoving means include a ring encircling the post, and means for moving the ring along the post to push a coil thereon off the post while the slide legs are squeezed together.

6. Apparatus in accordance with claim 2, in which said post is upright and the apparatus includes an intermittently movable support for the post for moving it laterally beneath a pair of slide legs at an assembly station and then laterally away from it, the post being slidably mounted in said support and extending below it, said axial movement effecting means include means beneath said support at the assembly station for raising the post into engagement with the lower ends of slide legs above it, and said coilmoving means include a ring encircling the post above said support, a stem connected to one side of the ring and slidably mounted in said support, and means beneath the support at the assembly station for raising said stem and ring to push a coil on the post up around said legs.

7. Apparatus according to claim 6, including means for guiding slides in succession to said assembly station and holding them there while coils are pushed onto their legs.

8. Apparatus according to claim 1, including means for holding a slide stationary adjacent the free end of the post, and said axial movement-effecting means including a device for moving the post into engagement with said free ends of slide legs.

9. Apparatus according to claim 2, in which said post is upright, and said coil-feeding means is an elongated member for slidably receiving a coil for axial movement along said member, said member being positioned above the post for guiding a coil down to the upper end of the post.

References Cited UNITED STATES PATENTS 3,122,826 3/1964 Self 29203X THOMAS H. EAGER, Primary Examiner 

